In a usual process of manufacturing beers, starch derived from ingredients including malt is hydrolyzed by hydrolases (α-amylase, β-amylase) and fermentable sugars such as glucose, maltose, and maltotriose, which a brewer's yeast can metabolize, and oligosaccharides larger than maltotetraose and dextrin are produced. The fermentable sugars are metabolized by a brewer's yeast and converted to the components of beer such as alcohol. It is said that oligosaccharides larger than maltotetraose and dextrin may remain in the beer without being metabolized and may participate in filling taste and fullness of mouthfeel of the beverages. Besides, isomaltooligosaccharides produced by α-glucosidase from malt may give filling taste and fullness of mouthfeel of the beer, but their concentrations are too low to influence the taste of the beer.
There is a method to increase the concentration of isomaltooligosaccharides by addition of isomaltooligosaccharides syrup in beers and high adjunct beer (Japanese Patent Application Publication No. 7-51045, Japanese Patent Application Publication No. 7-327659). In these methods, however, kinds and amounts of adjuncts are limited because it is essential to use isomaltooligosaccharides syrup as a adjunct. In addition, adjuncts are used in these methods, which means that these methods cannot be applied to the so-called all malt beers brewing.
On the other hand, a trial to reinforce filling taste and the like by using α-glucosidase in a method of manufacturing low alcohol beers has been performed. For example, in the method of manufacturing disclosed in Japanese Patent Application Publication No. 5-68529, there is an attempt to reinforce filling taste and the like by production of isomaltooligosaccharides through addition of α-glucosidase (another name; transglucosidase) to the boiling-treated wort in the wort production process. In detail, after wort boiling in the wort production process a ratio of the fermentable sugars in wort can be reduced by addition of α-glucosidase to wort in which the concentration may be adjusted not more than 10 weight %, so that filling taste of beers similar to that of the usual alcohol concentration beers may be given. In this method in which α-glucosidase is added after the concentration adjustment, however, there is the following problem. That is, α-glucosidase may remain in wort or fermented wort in the fermentation and maturating processes which follow the wort production process, and then, once produced, isomaltooligosaccharides may be hydrolyzed by the enzyme to glucose and then the concentration of isomaltooligosaccharides may be decreased.
Meanwhile, the following arts are known in the high gravity brewing of beers and in the low-calorie beer brewing. The high gravity brewing is a method to ferment the high concentration of original extract in manufacturing beers. Concretely, wort in which the concentration of original extract of wort is usually 13–16 weight % is fermented and matured, and the product is diluted with carbonated water to the designated concentration prior to shipping. The high gravity brewing has an advantage of enhancing productive efficiencies of manufacturing equipment such as fermentation and lagering tanks and curtailing energy costs. Therefore, it is widely used in European countries and the United States, whereas the problem that it takes a long time to ferment a great volume of wort extract is indicated. The method to promote the fermentation in the high gravity brewing includes (1) to accelerate the viability and growth of the yeast by supplying a great volume of oxygen, (2) to use fresh yeast, and (3) to supply free-amino nitrogen. Besides, there is a problem that beer flavor manufactured in the high gravity brewing may be different from that of beers in a usual method. Especially, the original extract of wort is high in the high gravity brewing, and since a brewer's yeast is exposed to conditions of high osmotic pressure, expression of acetaldehyde dehydrogenase gene is generally induced. Because acetic acid, an off-flavor of beers, is produced from acetaldehyde, it has been desired to reduce its production.
Meanwhile, low-calorie beer, also called as diet beer, is a general name of beers with low calories. According to the art of beer brewing, low-calorie beer is defined as that with carbohydrate at 0.75 g/100 g or less and with fermentation degree of 90–92%. On the other hand, light beer is a general name of beers having lighter flavor than that of usual beers. Although it is not standardized on the quality and the method of manufacturing, it has generally lower calories than that of usual beers and is counted as one of low-calorie beers. The method to manufacture low-calorie beers includes (4) to ferment using diluted wort less than 10 weight % of original extract, or to dilute usual beers produced from wort at 12–13 weight % of original extract, (5) to ferment highly using dextrin-hydrolyzing enzymes (glucoamylase, debranching enzyme, α-amylase derived from mold, malt enzyme etc.), (6) to use dextrin-metabolizing yeast including recombinant yeast, (7) to ferment highly by supplying glucose to wort, (8) to dilute beer manufactured through the high gravity brewing, and (9) to ferment separately not less than two kinds of wort with different concentrations of original extract, to mix them to make the concentration the designated one, and to re-ferment and mature and the like.
Enzymes from malt such as β-amylase are used to saccharify ingredients such as malt in the process of manufacturing beers. Then, because maltose is a major carbon-source in wort, a sake yeast and wine yeast other than a brewer's yeast, which are less able to metabolize maltose have not been able to be employed in the manufacturing beers.